1. Field of the Invention
This invention relates to a process for plugging porous earth formations. More particularly this invention relates to plugging an underground formation penetrated by a well bore, by pumping a shear-thickening fluid down the well bore to the site of the formation desired to be plugged and subjecting the shear-thickening fluid to high shear which instantly forms a stiff paste to plug said formation, wherein said process is characterized in that the water-in-oil emulsion portion of the shear-thickening fluid is used as a spacer to separate said fluid from drilling mud while same is pumped down the well bore.
2. Background of the Disclosure
During the drilling and production of wells, such as oil, gas or water wells, various problems sometimes occur which, if not corrected, result in the loss of considerable well production and even loss of the well itself. These problems include blow-outs, lost circulation and channeling. Blow-outs occur when the drill bit cuts into a high pressure zone of gas, oil, or water which can blow out the drilling mud and sometimes even the drill stem, bit and surface equipment resulting in their loss and destruction also. Lost circulation of drilling mud occurs when the drill bit cuts through a porous formation at a pressure such that drilling mud coming down the drill stem flows into the porous structure instead of being forced back up to the surface between the drill stem and well casing. Channeling occurs when a fluid in one porous formation flows through continuous passages in cement behind well casing into another porous formation at a different depth in the well.
A number of methods and compositions have been employed in order to solve these problems, none of which has met with complete success and, in fact, most have not been too successful. One method of trying to stop blow-outs involves loading up the well with a slurry of barite under pressure and under conditions such that the barite is able to settle uniformly at the bottom of the well to form a hard plug which may then be followed up with a cement slurry in order to make the plug more or less permanent. Various methods employed to stop lost circulation include slurries of barite along with fiberous, lumpy or flakey materials which it is hoped will ultimately form a filter cake and then a mat over the porous formation and thus plug up the channels. Another method used is to employ what is known as gunk which is a slurry of dry, powdered bentonite in diesel oil. When this material is mixed with the right amount of water, the bentonite will hydrate yielding a stiff paste. If formed at the right time and at the right place, this sometimes works as an effective lost circulation and well-plugging material. This type of material and method for its use is disclosed, for example, in U.S. Pat. No. 3,082,823. However, there are many problems associated with the use of this gunk. Among these problems is that the slurry must be kept dry until it reaches the desired formation in the well bore at which time it must be mixed with the proper amount of water in order to form a paste and not an emulsion or a slurry of hydrated benetonite.
U.S. Pat. No. 3,448,800 discloses a plugging method for restoring lost circulation in a well wherein a suspension or slurry of a particulate, water-soluble polymer in a non-aqueous medium is injected into a well. An aqueous slurry of a mineral material such as cement, barite or plaster of paris is separately injected into the well, with the two slurries meeting and mixing at the bottom of the well bore to form a plug at the area of lost circulation. U.S. Pat. No. 2,836,555 discloses a well plugging composition for restoring lost circulation in wells which comprises compressed, dehydrated pellets of bentonite encapsulated within a solid, water-insoluble polymeric coating which has a tiny hole drilled through the surface thereof. These pellets are pumped down into the well bore and, as they do so, water seeps into the hole in the coating into the bentonite thereby swelling and ultimately rupturing the coating. By proper design of the coating, etc., it is postulated that the pellets will rupture after they have become lodged in the lost circulation area to form a tight seal. U.S. Pat. No. 2,890,169 discloses another well control or lost circulation fluid which is made by forming a slurry of an organophilic bentonite and cement in oil. This slurry is mixed with a surfactant and water to form a composition comprising a water-in-oil emulsion having organophilic bentonite and cement dispersed in the continuous oil phase. As this composition is pumped down the well bore, the oil expands and flocculates the bentonite which, under the right conditions, forms a filter cake on the well bore surface in the porous area. This is then supposed to cause a filtration action which breaks the emulsion causing the emulsified water to react with the cement to form a solid coating on the filter cake thereby plugging the porous area.
One of the problems encountered with the use of organophilic clays, such as bentonite clays treated with quaternary ammonium compounds having at least one alkyl, alkylene or alkylidine radical, is that oil rapidly expands and disperses the clay at low shear rates. These organic modified clays are prepared from bentonite-type clays that are normally hydrophilic in nature. A typical organic modified clay is dimethyldihydrogenated tallow ammonium bentonite. These clays are used mainly as oil viscosifiers and dispersion aids and are not used as the plugging component of well control fluids.
It is known to those in the art that if one can mix a hydrophilic or water expandable clay, such as bentonite, with the proper amount of water in the presence of a water-soluble polymer which will flocculate and congeal the clay, a much stronger and stiffer paste can be made than that which will occur if the bentonite is merely mixed with water. Thus, U.S. Pat. No. 3,909,421 discloses a high viscosity fluid useful in secondary oil recovery processes. This fluid is made by physically blending a dry powdered, polyacrylamide with bentonite followed by mixing the powder blend with water. U.S. Pat. No. 4,128,528 claims a powdered bentonite-polyacrylamide thickening composition prepared by mixing a water-in-oil emulsion with bentonite to form a damp, free-flowing powdered composition which rapidly forms a viscous, stiff material when mixed with water. The dispersed aqueous phase of the emulsion contains a water soluble surfactant along with a dispersion and/or solution of a water soluble polymer formed in-situ in the emulsion. The water-soluble polymer may be polyacrylamide or a copolymer of acrylamide and acrylic or methacrylic acid. This composition is taught as being useful for drilling muds, bases for earthen dams and clay cements.
Although many efforts have been made in an attempt to use bentonite-water systems with or without a water-soluble polymer which will flocculate and congeal the bentonite, one of the main problems has been to keep the bentonite away from the water until same reaches the desired part of the well bore, which is usually at the bottom. Another problem has been making sure that the bentonite mixes with the proper amount of water to rapidly form a stiff paste or cement at the location of the problem in the well.
An attempt to overcome these difficulties has been made by dispersing bentonite into the continuous, oily phase of a water-in-oil emulsion formulated to have a proper balance of water and bentonite and also formulated to keep the bentonite and water apart until the dispersion is forced through the nozzles of the drill bit at the bottom of the well. Thus, copending application Ser. Nos. 79,436 (abandoned) and 79,437 (abandoned) filed on Sept. 27, 1979 and Ser. No. 79,978 (abandoned) filed on Sept. 28, 1979 disclose shear thickening well control fluids which comprise bentonite dispersed in the continuous, oily phase of a water-in-oil emulsion. The oily phase contains a surfactant and the dispersed, aqueous phase may or may not contain a water-soluble polymer, such as a polyacrylamide, for congealing and flocculating the clay. These well control fluids have met with some success in solving some of the problems discussed above. However, it has recently been discovered that drilling mud, oil or water directly contacting the shear thickening fluid in the drill pipe has an adverse effect on the paste that is ultimately formed from the shear thickening fluid itself.